Electrical protective system



Feb. 29, 1944. s. H. cowm 2,342,845

ELECTRICAL PROTECTIVE SYSTEM- Filed Jan. 9, 1941 3nventor zzmi 97.(011/220 (Ittorneg Patented Feb. 2?, 1944 I UNITED STATES PATENT OFFICE2,342,845 ELECTRICAL PROTECTIVE SYSTEM Stuart H. Cowin, Chicago, Ill.,assignor to General Motors Corporation, Detroit, Mich., a corporation ofDelaware Application January 9, 1941, Serial No. 373,716 9 Claims. (Cl.175-294) My invention relates in general to electrical effectiveness ofthe relay by connecting it in low protective systems and moreparticularly to an resistance relationship with both sides of theimproved arrangement of leakage current responpower circuit.

sive ground protective means in an electrical cir- Another object is theprovision of means concuit to increase the effectiveness and efiiciencytrolled by the protective means to open the genof such protectivesystems. erator load circuit and simultaneously to reduce Inconventional systems of this type the prothe voltage of the generator tosubstantially zero,

tective means is generally connected in equiso that no one may receivean electrical shock potential relation between both sides of the powertherefrom, providing adequate protection Of the circuit and ground bybeing connected between 10 electrical means against damage from ou dsground and the mid-point of a resistor which is and flashover and of thepersonnel against shocks. connected directly across the power line andac- The combination of the protective means and cordingly constitutes acontinuous power loss. its arrangement in relation with the generator Toreduce this continuous power loss, the resistand power circuits by whichthe above objects are ance of this shunt resistor is made high andaccomplished will be better understood by refertherefore greatly limitsthe current through the ring to the single diagrammatic drawingllluscurrent responsive protective means to a low trating my improvedprotective system and the value. The current responsive means used withfollowing detailed description thereof. this arrangement is, therefore,usually a gal- Referring now to the drawing, the power circuit vanometerrelay which controls power operated includes a generator G having anarmature A, a circuit breakers or isolation switches to open a motor Mand power operated contactors SI and section of the power line should aground occur $2 for os n a Opening h s es o t e Dower therein. circuitcomprising the power conductors l and 2 On prime mover generator powerplants, parby which the motor is connected to the generator ticularlythose where the load demand is subupon closure of the switches SI andS2. The stantially equal to the rated load of the prime armatureAof thegenerator may be driven by any mover and generator, such as those usedon electype of variable speed prime mover and the motor trically drivenvehicles, it is desirable to protect M constituting the electrical loadon the generator 7 the generator as well as the load circuit against maybe connected in any well known manner to grounds, and also to insurethat no one will redrive a load such as the wheels of a vehicle. Ifceive an electrical shock from the generator or a plurality of motorsare used the contactors SI load circuit when a ground occurs in any partand S2 may be arranged to connect the motors of the power system. Itwill be evident that conin either a series or parallel relation with thevcntional systems in which only the load circuit generator inconventional manner. is disconnected from the generator when a ground erat r G s ShOWIl P d d t S occurs in the load circuit do not provideadequate and separately excited excitation circuits, couprotection ofthe generator for grounds occurring stituting the means whereby thevoltage and out in the circuit between the generator and load cirput ofthe generator are regulated. cult disconnecting mean or protectionagainst The self or shunt excitation circuit, shown, in-

shocks from the generator. cludes a shunt field winding SF and rheostatsWith myimproved arrangement a single power- SR! and SR2 connected inseries across the power fui current responsive relay is connected withthe line conductors i and 2. A power operated congenerator circuit sothat all parts of the generator tac SS is provided to normally shunt outthe and the load circuit are equally protected against resistor SR2 ofhigh resistanc so that normal grounds and flashover of the generator ormotors shunt excitation current flows in the shunt exin'cluded in theload circuit upon leakage of curcitation windings SF. The shuntexcitation current to ground from any part of the generator or rent inthis circuit, therefore. is normally limited load circuit. Thisconstitutes the principal object by only the resistance of the windin SEand of my invention. that of the rhcostat SRi, both of these resistancesAnother object resides in combining the curbeing of low value. Adifferential series field rent responsive relay as part of the generatorgenerator winding may also be provided if deshunt excitation circuit,thus eliminating the sired. However, it is not shown. The rhcostat usualcontinuous power loss present in conven- SRI is the conventional fixedresistor usually tional arrangements and increasing the efllciencyplaced in series with the shunt field winding SF of the protectivesystem and also increasing the Of generators to enable the size of theshunt shown provided with field coil windings to be reduced, and thisresistor is usually provided with suitable taps to vary its resistanceslightly in order to obtain the proper excitation current through theshunt field coils. which usually vary slightly in resistance due tomanufacturing difierences, so that rated generator voltage and outputare obtained.

The separately excited excitation circuit includes a field winding BF,an adjustable rheostat BR, a manually operable control switch CS and apower operated contactor BS. The control switch CS, together with theprotective means to be described, serves to control'the contactors SSand BS, the latter serving to connect or disconnect the separatelyexcited field winding to a battery B and to connect this winding to adischarge resistor DR when disconnected from the battery.

Each of the contactor SI, S2, SS and BS is fixed contacts, and one ormore contacts fixed to an armature which are movable upward from theposition r-hown by an electromagnetic actuating coil. Energization andde-energization of these coils are controlled jointly by protectivemeans-acting automatically in response to leakage current from any partof the power circuit, shown as a relay GR, and the manually operablecontrol switches CS and PS. It will be evident that these contactors maybe operated by means other than the electromagnetic means shown.

The relay GR is provided with fixed contacts and contacts shown bridgingthe fixed contacts which are fixed to an armature which is movableupward from this position upon energization of the electromagneticactuating coil also shown. The connection of this coil between groundand the shunt excitation circuit, to be described, permits ampleattractive force to be exerted by the coil on the armature. Holding ordetent means, shown schematically at H, is provided to retain the relayarmatur in tion. This means includes a detent groove in the armature andstationary resilient detent fingers placed so that they will enter the'detent groove when the armature is moved to its open position. Movementof the armature of the relay back to its closed position is accomplishedmanually. A disconnectin switch DS is provided in series with theactuating coil to cause deenergization thereof so that the be movedmanually downward to its closed position' in which it is shown.

The energization and control connections ex tending between the abovedescribed contactors, switches, relay and generator shunt excitationcircuit will now be described. a

The rheostats SRI, SR2 and shunt field winding SF, as has beenpreviously described, are connected in series across the power lineconductors I and 2 and, as shown, conductors 3 and 4 serve to connectthe rheostat SR2 across the fixed contncts of the conductor SS.

The separately excited shown connected in series with the battery B, thecontrol switch CS, the upper pair of fixed contacts of conductors 5, I,9, BS is provided with an additional lower pair of fixed contacts shownbridged by the armature contact. One of the lower andone of the upperfixed contact are connected to th conductor 9 its upward or openposiarmature ma then.

field winding BF is.

the contactor BS and rheostat BR by II, I3 and I5. The contactor and adischarge resistor DR is connected between the other lower fixed contactof the contactor BS and the conductor I5.

The electromagnetic actuating coils of the contactors SS and BS areconnected in parallel by conductors I1 and I9, the conductor i'I beingconnected to the conductor I and the conductor I9 being connected by aconductor 2I to the upper right hand fixed contact of the. relay GR, theleft upper and lower contacts of which are connected to the conductorI5.

The electromagnetic actuating coils of the line contactors SI andSZ areconnected in parallel by conductors 23 and 25, the conductor 25 beingshown connected to the right lower fixed contact of the relay GR by aconductor 21 and the conductor 23 being shown connected to one contactof the control switch PS, the other contact of which is connected to theconductor 5.

The actuating coil of 'the relay GR has one terminal connected togroundat 29 and the'other terminal is connected by a conductor 3I to theconductor 3.

The operation of the protective system with the switches, contactors andrelay in the position is as follows:

Closure of the manually operable control switch CS causes energizationof the actuating coils of the contactors SS and BS from the battery Bthrough the conductors 5, I, I1, I9, 2| and I5, which causes upwardmovement of their armatures into bridging relation with the upper fixedcontacts thereof. Bridging of the fixed contacts of contactor SS shuntsthe resistor SR2 of high resistance out of the generator shuntexcitation circuit, and the bridging of the upper pair of fixed contactsof contactor BS connects the separately excited field winding BF andrheostat BR in series with the battery through conductors 5, I, 9, II,I3 and I5. 7

Closure of the manually operable ,control switch PS causes energizationof the coils of the line contactors SI and S2 through conductors 5, 23,25, 2! and I5, which causes upward movement of their armatures to bridgethe fixed contacts thereof to connect the.motor M across the generator Gthrough the conductors I and 2 constituting the power line.

With the contactorsSS, BS, SI and S2 closed and the armature A of thegenerator driven at some selected speed by the prime mover, the outputof the generator is regulated by both the shunt and separately excitedfield windings of the generator. The excitation current in both windingsis regulated by the adjustable rheostat BR to regulate the generatoroutput. Variations in the prime move! and generator output to satisfyvariations in the power demand by the of the generator and motor, thenormal position v of the armature of the relay being as shown. Should,however, a ground or fiashover to ground occur in any part of the motor,generator or power circuit. the current leakage to ground will flowthrough the actuating coil of the relay with the coil connected asshown. Assuming that a ground occurs on the power conductor I, leakagecurrent will flow between conductors I and'2 through the coil of therelay and rheostat SRI in series therewith as one side of the relay coilposition. Upon repair of the is'groundcd and the rheostat SR2 isnormally shunted. The shunt field winding SF is accordcircuit to obtainequal response to grounds in any part of the circuit. It will likewisebe evident that leakage current to ground caused by a flashshown.

charge resistor DR is connected directly across the separately excitedfield winding BF upon the circuits may be tested for grounds while inthis the relay armature is moved downward normally to its normalposition, as shown.

As previously mentioned the generator G may be provided with adifferential series field windrounded conductor that my protectivesystem and arrangement operates without power loss as long as the powercircuit and electrical trical shocks.

I claim: r 1. In a protective system of the type described comprising agenerator voltage to a low value, a generator load circuit includingdisconnecting means, and current responsive protective control generatoror load circuit.

2. In a protective system of the type described comprisinga generatorhaving a shunt excitation circuit which includes both inductance andresistance and a separately excited excitation circuit-including meansfor opening said circuit, a load circuit for said'generator having meansfor opening said circuit, and current responsive pro tective meansconnected between ground and a point in said generator shunt excitationcircuit which is normally at equipotential relation with the generatorterminals so that it acts with equal response to leakage current fromsaid power circuit or generator to simultaneously control themeans foropening the separately excited excitation circuit and the means circuitso that the voltage of said generator is substantially reduced,rendering both the generator and the power circuit safe againstelectrical grounds or electrical shock due to grounds.

} 3. In a ground protective system for electrical circuits comprising acompound generator having shunt and separately excited excitationcircuits, excitation reducing means in each of said circuits operablefor causing the voltage and output of the generator to be reduced tosubstantially zero voltage, a current responsive relay including anactuating coil having one side grounded, an armature movable by saidcoil upon energization thereof to control operation of said excitationreducing means in said generator excitation circuits, means forretaining said armature in the position to which it is moved by saidcoil, and means operable at will for connecting the other side of saidcoil to a point in said shunt excitation circuit where the normalpotential difference between said point and each of said generatorterminals is substantially equal whereby it is energized only by leakageof current to ground from any part of said generator caused bydefeceither side of said a resistance substantially equal all connectedin series operable switching a and operable to insert all of saidresistance in series with said winding toreduce the generator voltage toa low value, and leakage current responsive means connected betweenground and the portion of the resistance normally shunted i orcontrolling operation of said switchingmeans.

5. In a protective system of the type described comprising a generatorhaving a shunt excitation circuit including an excitation winding, 9.resistance in series therewith, switching means normally shunting aportion of said resistance connect'ed adjacent the excitation winding,said switching means being operable to insert all of said resistanceinsaid circuit, .an external generator load circuit including switchingmeans for opening said load circuit, and current responsive meansconnected between ground and said portion of the resistance normallyshunted so that said current responsive means is adapted to act onlyupon leakage of current to ground from generator and external loadcircuit to control operation of both said switching means therebycausing a substantial reductionin the generator voltage and opening theload circuit.

6. In an electrical protective system of the type described comprising agenerator having a shunt excitation circuit and a'separate excitationcircuit, the shunt excitation circuit comprising a low resistance fieldwinding, a resistance unit of to that of the field and a resistance unitof high resistance,

relation, and also a contactor operable to shunt the high resistanceunit, the separate excitation circuit comprising a field winding, afield rheostat, a separate source of current and a contactor, allconnected in series, said last named contactor being operable tocomplete the separate excitation circuit, and control means forcontrollingoperation of all of said contactors comprising seriesconnected manually windin switching means, said current operatedswitching means having a current operating coil connected between groundand the common connection between the high and low resistance units forenergizing only by any slight leakage of current from either of thegenerator terminals to ground to cause operation of the current operatedswitching means to render the manually operable switching meansincapable of controlling normal operation of said contactors and therebysimultaneously to cause insertion of the high resistance unit in theshunt field circuit and opening of the separately excited circuitindependently of the manuallyoperable control means.

7. In an electricalprotective system of the type described comprising agenerator.-a load circuit therefor comprising a motor and contactorsoperable for connecting both generator terminals to both sides of theload circuit or' disconnecting them therefrom. excitation means for saidgenerator comprising a shunt excitation circuit and a separately excitedexcitation circuit,.the shunt means and current operated the shuntexcitation circuit to act only in response excitation circuit comprisinga low resistance field ance, the other portion of the resistance beingsubstantially equal to the resistance of said winding, the separatelyexcited excitation circuit comprising a field winding, a separate sourceof current and a contactor operable for connecting the source of currentto the circuit or disconnecting it therefrom, and means for controllingall of said contactors, said control means comprising manually operablemeans and current responsive means said current responsive meansconnected between ground and the common connection between the fieldwinding and the resistance in to leakage ofcurrent from any part of saidgenerator or said generator load circuit, said current responsivecontrol means being connected to said manually operable control means insuch manner that when there is no leakage of current to ground thecurrent responsive means is inactive and then permits the contactors tobe normally controlled by said manually operable control means, but uponleakage of current to ground the current responsive means actsautomatically to render the manually operable control means inefiectiveto control operation of said. contactors, which causes all of saidresistance to be inserted in the shunt excitation circuit and causesboth the separately excited excitation circuit and both sides of thepower circuit to .be opened.

8. In a protective system of the type described comprising a loadcircuit including a generator, connecting means for connecting bothsides of said load circuit across the generator, a generator excitationcircuit connected in shunt relation with the load circuit, saidexcitation circuit comprising an exciting winding, a resistance inseries therewith, and shunting means normally shunting the major portionof the resistance to permitnormal excitation of the generator, and aground protective means having an actuating winding,

.means movable to an operative position by the tion and means forconnecting said actuating winding of said protective means betweenground and the common connection between the field winding and theresistance in the generator shunt excitation circuit for energization byleakage of current to ground from either side of said generator or saidcircuits nergized thereby, said connecting means for said actuatingwinding including a manually operable disconnecting switch.

9. In a protective system of the type described comprising a compoundgenerator having shunt and separately excited excitation circuits, theshunt excitation circuit comprising a low resistance excitation winding,a resistor of substantially the same resistance as the excitationwinding, a discharge resistor of high resistance. said resistors beingconnected in series. and a contactor connected across the dischargeresistor which is operable to shunt the discharge resistor, theseparately excited excitation circuitcomprising an excitation winding.2. rheostat, a discharge resistor, a separate source of current, and acontactor normally connecting the separate excita tion winding. rheostatand discharge resistor in series, said second mentioned contactor beingoperable to disconnect the discharge resistor and to connect theseparate excitation winding and rheostat to said separate source ofcurrent, a generator power circuit including contactors operable toconnect both sides of the power circuit to the generator, seriesconnected manually operable means and current responsive means forcontrolling operation of all of said contactors, means for connectingsaid current responsive means between ground and the generator shuntexcitation circuit so that it acts only upon enercurrent from any partof said generator or any part of any circuit supplied i by saidgenerator to render said coniacmrs inoperable independently of saidmanually operable control means but normally allowing ontiol andoperation thereof by said manuall operable means when there is noleakage of current from the power circuit, said current responsive meansbeing provided with holding means to retain said current responsivemeans in the active position STUART Hi COWTN.

